1. Field of the Invention
The present invention relates to an apparatus and a method for changing a mode in a proportional integral differential controller (hereinafter, referred to as a PID controller). More specifically, the present invention relates to an apparatus and a method for changing a mode in a PID controller, which can remove an impact generated in a mode change and stably perform the mode change when the operational mode of the PID controller is changed from a manual mode to an automatic mode or vice versa.
2. Description of the Related Art
In general, a PID controller is widely used to control the driving of various types of loads including an electric motor and the like. The operational modes of the PID controller that drives a load are divided into an automatic mode and a manual mode.
In the automatic mode, the PID controller determines the current state of the load by inputting a speed detection signal to the load, and generates a driving signal for driving the load by PID-controlling the determined state of the load and a speed command signal set by a user. Then, the PID controller drives the load based on the generated driving signal.
Thus, the automatic mode is used to drive the load in a state desired by the user according to the current operational state of the load, and the PID controller can stably drive the load by repeatedly performing an operation without a pause.
In the manual mode, the PID controller drives the load by generating a driving signal based on the speed command signal set by the user, regardless of the state of the load fed back from a system.
The automatic and manual modes of the PID controller can be changed when the user so desires. However, in a case where a mode change is performed in the state that the load is driven based on an output signal of the PID controller, an overload is applied to the system, and an impact is generated due to the mode change.
For example, in a case where the operational mode of the PID controller is changed from the automatic mode to the manual mode, the PID controller outputs a driving signal based on only the speed command signal in the state that the PID controller outputs the driving signal according to the difference value between the speed detection signal and the speed command signal.
If the value of the driving signal outputted from the PID controller is greatly changed, the driving state of the load is greatly changed, and the change in the driving state of the load is transferred to the system as it is. Therefore, an overload is applied to the system.
Thus, in a case where the operational mode of the PID controller is changed from the automatic mode into the manual mode, the generation of an impact generated in the mode change is restricted by limiting the variation of a driving signal outputted from the PID controller, and accordingly, the overload of the system is prevented.
However, if the variation of the driving signal outputted from the PID controller is limited in the mode change, a response speed is delayed.
Further, in a case where the operational mode of the PID controller is changed from the manual mode into the automatic mode, the PID controller performs a PID control from an initial value, and hence it takes much time for the PID controller to drive a load in a stable state. Therefore, the driving speed of the load is not constantly stable, and accordingly, the system is vibrated.